Sorghum is the fifth largest crop worldwide. It is a genus comprised of numerous species of grasses, some of which are raised for the production of biofuels, foods, grains, alcoholic beverages and other useful products. The plants are cultivated in warmer climates worldwide, and several species are native to tropical and subtropical regions of all continents. Several species are drought tolerant and heat tolerant, and are especially important in arid regions.
440,000 square kilometres were devoted worldwide to Sorghum production in 2004, but little research has been done to improve Sorghum cultivars because the vast majority of Sorghum production is done by subsistence farmers. The crop is therefore mostly limited by insects, disease and weeds, rather than by the plant's inherent ability.
Sorghum's growth habit is similar to that of maize, but with more side shoots and a more extensively branched roof system. The root system is fibrous, and can extend to a depth of up to 1.2 m. The plant finds 75% of its water in the top meter of soil, and because of this, in dry areas, the plant's production can be severely affected by the water holding capacity of the soil.
Sorghum is well adapted to growth in hot, arid and semi-arid areas. The many subspecies are divided into four groups—grain sorghums (such as milo), grass sorghums (for pasture and hay), sweet sorghums (formerly called “Guinea corn”, used to produce sorghum syrups), and broom corn (for brooms and brushes). The name “sweet sorghum” is used to identify varieties of S. bicolor that are sweet and juicy.
Sorghum bicolor is the primary Sorghum species cultivated for grain for human consumption and for animal feed. The species originated in northern Africa and can grow in arid soils and withstand prolonged droughts. Sorghum bicolor is usually an annual, but some cultivars are perennial. It grows in clumps which may reach over 4 meters high. The grain is small, reaching about 3 to 4 mm in diameter. Sorghum is source of ethanol biofuel, and in some environments may be better than maize or sugarcane because it can grow under more harsh conditions.
Sorghum is one of the most efficient grains for producing ethanol with a typical starch content and ethanol yield as compared to other grains of:
StarchEthanol(% dry basis)(liters per ton)Sorghum74400Corn70385Wheat65350Barley60321(See P. Wylie, P. Searching For the Facts on Ethanol. 2005).
Recently, the US Congress passed a Renewable Fuels Standard as part of the Energy Policy Act of 2005, with the goal of producing 30 billion liters (8 billion gallons) of renewable fuel (ethanol) annually by 2012. This bill should noticeably increase the demand for ethanol producing crops for at least the next decade. Sorghum growers are predicting that this will stimulate demand for Sorghum production.
Despite the many advantages that Sorghum has as an energy crop, in order for this grass to fulfill its promise, new varieties of Sorghum are needed that will have increased hardiness and yield, reduce the need for nitrogen and other chemical fertilizers, and allow propagation under widely variant growing conditions. For instance, Sorghum is a very high nitrogen feeding crop. An average hectare producing grain requires 110 kg of nitrogen. Compacted soil or shallow topsoil can also limit the plants ability to deal with drought by limiting its root system. Moreover, some species of Sorghum can contain toxic levels of cyanide and nitrates lethal to grazing animals in the early stages of the plant's growth as well as under stress conditions.
Plants specifically improved for energy usage can be obtained using molecular technologies. Manipulation of crop performance has been accomplished conventionally for centuries through plant breeding. The breeding process is, however, both time-consuming and labor-intensive. Furthermore, appropriate breeding programs must be specially designed for each relevant plant species.
On the other hand, molecular genetics approaches that introduce and express recombinant nucleic acid molecules allow production of plant species tailored to grow more efficiently and produce more product in unique geographic and/or climatic environments. To this end, in some aspects the present invention is directed to advantageously manipulating plant characteristics in traits such as architecture, biomass, development, composition, conversion efficiency, energy output, confinement, nitrogen use, nutrient uptake, phosphate use, photosynthetic capacity, shade avoidance, cold tolerance, drought tolerance, water use efficiency, stress tolerance, vigor, flowering time and yield to maximize the benefits of energy crops and other economically important crops depending on the benefit sought and the particular environment in which the crop must grow. These molecules may be from the plant itself, and simply expressed at a higher or lower level, or the molecules may be from different plant species.